US9548357B2 - Shallow trench isolation structure with sigma cavity - Google Patents
Shallow trench isolation structure with sigma cavity Download PDFInfo
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- US9548357B2 US9548357B2 US14/716,696 US201514716696A US9548357B2 US 9548357 B2 US9548357 B2 US 9548357B2 US 201514716696 A US201514716696 A US 201514716696A US 9548357 B2 US9548357 B2 US 9548357B2
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- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
- H01L29/0603—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions characterised by particular constructional design considerations, e.g. for preventing surface leakage, for controlling electric field concentration or for internal isolations regions
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- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
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Definitions
- the present invention relates generally to semiconductor fabrication, and more particularly, to shallow trench isolation structures and methods of fabrication.
- Transistors are commonly used in the integrated circuits (ICs).
- ICs integrated circuits
- carrier mobility e.g., electrons or holes
- strain engineering has been applied since the 90 nm complementary metal-oxide semiconductor (CMOS) node.
- CMOS complementary metal-oxide semiconductor
- inducing a tensile strain in the channel of n-type transistors improves electron mobility while a compressive strain in the channel of p-type transistors improves hole mobility.
- CMOS complementary metal-oxide semiconductor
- CMOS complementary metal-oxide semiconductor
- inducing a tensile strain in the channel of n-type transistors improves electron mobility while a compressive strain in the channel of p-type transistors improves hole mobility.
- Various techniques have been proposed to induce the desired stress in the channel region of transistors.
- transistors are scaled to smaller dimensions, there is a need for higher carrier mobility for
- Embodiments of the present invention provide an improved shallow trench isolation structure and method of fabrication.
- the shallow trench isolation cavity includes an upper region having a sigma cavity shape, and a lower region having a substantially rectangular cross-section.
- the lower region is filled with a first material having good gap fill properties.
- the sigma cavity is filled with a second material having good stress-inducing properties.
- source/drain stressor cavities may be eliminated, with the stress provided by the shallow trench isolation structure.
- the stress from the shallow trench isolation structure may be used to complement or counteract stress from a source/drain stressor region of an adjacent transistor. This enables precise tuning of channel stress to achieve a desired carrier mobility for a transistor.
- embodiments of the present invention provide a semiconductor structure, comprising: a semiconductor substrate; a cavity formed in the semiconductor substrate, the cavity comprising an upper region and a lower region, wherein the upper region comprises a sigma cavity, and the lower region comprises a substantially rectangular cavity; a first dielectric layer disposed in the lower region; and a second dielectric layer disposed in the upper region, wherein the second dielectric layer is planar with a top surface of the semiconductor substrate.
- embodiments of the present invention provide a semiconductor structure, comprising: a semiconductor substrate; a transistor disposed on the semiconductor substrate, the transistor comprising a source/drain region and a gate; a shallow trench isolation structure disposed adjacent to the source/drain region, the shallow trench isolation structure comprising: a cavity formed in the semiconductor substrate, the cavity comprising an upper region and a lower region, wherein the upper region comprises a sigma cavity, and the lower region comprises a substantially rectangular cavity; a first dielectric layer disposed in the lower region; and a second dielectric layer disposed in the upper region, wherein the second dielectric layer is planar with a top surface of the semiconductor substrate.
- embodiments of the present invention provide a method of making a semiconductor structure, comprising: performing a first anisotropic etch in a semiconductor substrate to form a cavity; performing a sigma etch on the cavity to form an upper region of the cavity; performing a second anisotropic etch to form a lower region of the cavity; filling the lower region of the cavity with a first material; filling the upper region of the cavity with a second material; and planarizing the second material to a level flush with a top surface of the semiconductor substrate.
- FIG. 1 is a semiconductor structure at a starting point for embodiments of the present invention.
- FIG. 2 is a semiconductor structure after a subsequent process step of forming a sigma cavity in an upper region of a shallow trench isolation cavity in accordance with embodiments of the present invention.
- FIG. 3 is a semiconductor structure after a subsequent process step of forming a lower region of a shallow trench isolation cavity in accordance with embodiments of the present invention.
- FIG. 4 is a semiconductor structure after a subsequent process step of depositing a first fill material.
- FIG. 5 is a semiconductor structure after a subsequent process step of recessing the first fill material.
- FIG. 6 is a semiconductor structure after a subsequent process step of depositing a second fill material.
- FIG. 7 is a semiconductor structure after a subsequent process step of recessing the second fill material.
- FIG. 8 is a semiconductor structure including three fill materials in accordance with alternative illustrative embodiments.
- FIG. 9 is a semiconductor structure in accordance with embodiments of the present invention including a transistor.
- FIG. 10 is a semiconductor structure in accordance with alternative embodiments of the present invention including a transistor.
- FIG. 11 is a flowchart indicating process steps for embodiments of the present invention.
- first element such as a first structure, e.g., a first layer
- second element such as a second structure, e.g. a second layer
- intervening elements such as an interface structure, e.g. interface layer
- FIG. 1 is a semiconductor structure 100 at a starting point for embodiments of the present invention.
- Semiconductor structure 100 includes a substrate 102 and a shallow trench isolation (STI) cavity 104 disposed in the substrate 102 .
- substrate 102 may be a silicon (Si) substrate, silicon germanium (SiGe) substrate, or another suitable substrate.
- a protective layer 106 is deposited over the substrate 102 .
- protective layer 106 may include a nitride such as silicon nitride (SiN), often referred to as hard mask.
- FIG. 2 is semiconductor structure 100 after a subsequent process step of forming a sigma cavity 108 in an upper region 111 (see FIG. 3 ) of the shallow trench isolation cavity 104 in accordance with embodiments of the present invention.
- Sigma cavity 108 is formed as a result of, for example, employing a fast etch-rate on the bottom surface which has a crystalline plane of (100) of cavity 104 by anisotropic wet-etching (e.g., utilizing tetramethylammonium hydroxide (TMAH), ammonium hydroxide, and/or potassium hydroxide).
- TMAH tetramethylammonium hydroxide
- ammonium hydroxide and/or potassium hydroxide
- FIG. 3 is semiconductor structure 100 after a subsequent process step of forming a substantially rectangular cavity 112 in lower region 113 of a shallow trench isolation cavity 104 in accordance with embodiments of the present invention.
- rectangular cavity 112 may have a slight taper (not shown) as a result of vertical anisotropic plasma etching (e.g. Cl-chemistry based plasma etching).
- FIG. 4 is a semiconductor structure 100 after a subsequent process step of depositing a first fill layer 114 .
- the first fill layer 114 may be a dielectric.
- the first fill layer 114 may include spin-on dielectric, spin-on glass, or flowable oxide or another dielectric deposited by CVD (chemical vapor deposition) methods.
- the first fill layer 114 preferably has a superior capability of gap-fill as the trench cavity has a small top critical dimension (CD) and depth (i.e., the largest aspect ratio).
- CD critical dimension
- SOD spin-on dielectric
- the high density plasma (HDP) CVD oxide, HARP (high-aspect-ratio process) oxide, or enhanced high-aspect-ratio process (eHARP) oxide has reduced capability to gap-fill the trench (with small CD and large aspect ratio) but increased residual stress.
- FIG. 5 is a semiconductor structure 100 after a subsequent process step of recessing the first fill layer 114 .
- the recessing can be achieved a by hydrofluoric (HF) etch, or (SiCoNi) process, or CMP, or a combination of these.
- FIG. 6 is a semiconductor structure 100 after a subsequent process step of depositing a second fill layer 116 .
- the second fill layer 116 may include high density plasma (HDP) CVD oxide, silicon oxide, or HARP oxide.
- the depositing may be achieved by other chemical vapor deposition (CVD) methods.
- the second fill layer 116 does not require strong gap fill properties as needed with first fill layer 114 (see FIG. 5 ) because the aspect ratio of the upper region 111 is reduced.
- FIG. 7 is a semiconductor structure 100 after a subsequent process step of recessing the second fill layer 116 .
- the recessing causes the second dielectric fill layer 116 to be exposed and planar with a top surface of protective layer 106 .
- the recessing may be performed by chemical mechanical polishing (CMP).
- the semiconductor structure includes a semiconductor substrate 102 ; a cavity 104 formed in the semiconductor substrate, the cavity 104 including an upper region 111 and a lower region 113 , wherein the upper region includes a sigma cavity 108 , and the lower region 113 includes a substantially rectangular cavity 112 ; a first dielectric layer 114 disposed in the lower region; and a second dielectric layer 116 disposed in the upper region, wherein the second dielectric layer 114 is planar with a top surface of a protective layer 106 over the substrate 102 .
- the cavity 104 has a depth D 1 .
- D 1 may range from about 100 nanometers to about 300 nanometers.
- the width of cavity 104 is continuously scaled to less than ⁇ 30 nm-50 nm at advanced complementary metal-oxide semiconductor (CMOS) node (e.g., 20 nm).
- CMOS complementary metal-oxide semiconductor
- Each of tips 110 a and 110 b has an angle A. In embodiments, A may be 109.4 degrees.
- the tips are disposed at a distance D 2 below the top surface of the substrate 109 .
- Each of the tips 110 a and 110 b serves as a concentrator of the residual stress in the upper portion 111 of STI trench cavity 104 and can re-direct the stress laterally into the Si with peak stress positioned at a distance of D 2 below the top surface of the substrate 109 (i.e., the position of the inversion charge carriers in the transistor channel).
- D 2 ranges from about 6 nanometers to about 8 nanometers.
- FIG. 8 is a semiconductor structure 200 including three fill layers in accordance with alternative illustrative embodiments.
- Semiconductor structure 200 includes a semiconductor substrate 202 ; a STI cavity 204 formed in the semiconductor substrate 202 , the cavity 204 comprising an upper region 211 and a lower region 213 , wherein the upper region 211 comprises a sigma cavity 208 , and the lower region 213 comprises a substantially rectangular cavity 212 .
- three layers are disposed in the cavity 204 for the more advanced cavity 204 with small top CD and depth (as compared to the two layers of the embodiment of FIG. 7 ).
- dielectric layer 215 is deposited into cavity 204 , followed by dielectric layer 214 above dielectric layer 215 , and then dielectric layer 216 is deposited above dielectric layer 214 .
- a protective layer 206 is the hard mask layer over the substrate 202 .
- protective layer 206 may include a nitride such as silicon nitride (SiN). All other method steps to form the semiconductor structure of this embodiment are similar to those of FIGS. 1-7 .
- the layer 214 may include a CVD oxide; the layer 216 may include a HARP oxide; and the layer 215 may include a flowable oxide, spin-on glass, or spin-on dielectric.
- the dielectric layers are progressively easier to fill in the trench cavity 214 (i.e., the aspect ratio of cavity is progressively reduced toward the deposition of the last layer 216 ).
- the last (i.e., top) layer 216 for gap-fill can use the HDP method with the highest mechanical hardness and strain, though the least gap-fill capability.
- This embodiment is designed for an advanced STI cavity with smaller top CD and deeper depth (than FIG. 7 ) for future generations of CMOS.
- the STI trench filling can be more than three layers at the cost of process complexity.
- the tips serve as a concentrator and re-direct the residual stress in the upper portion of STI trench laterally into the substrate with peak stress positioned at the same level of the inversion carriers in the transistor channel.
- FIG. 9 is a semiconductor structure 300 in accordance with embodiments of the present invention including a transistor.
- Semiconductor structure 300 includes a semiconductor substrate 302 and transistor 320 disposed on the semiconductor substrate 302 .
- the transistor 320 includes a gate stack 324 and source/drain regions 322 a - b without stressor material.
- the gate stack 324 includes a gate 330 over a gate dielectric 332 , such as silicon oxide, hafnium oxide, or zirconium oxide, and spacers 334 a and 334 b at each side of the gate 330 and gate dielectric 332 .
- the spacers can include a nitride or oxide such as silicon nitride or silicon oxide.
- a shallow trench isolation structure is disposed adjacent to the source/drain region 322 a .
- the shallow trench isolation structure includes a cavity 304 formed in the semiconductor substrate 302 , the STI cavity 304 comprising an upper region 311 and a lower region 313 .
- the upper region comprises a sigma cavity 308
- the lower region 313 comprises a substantially rectangular cavity 312 .
- a first dielectric layer 314 is disposed in the lower region 313
- a second dielectric layer 316 is disposed in the upper region 311 , and is planar with a top surface of the substrate 302 .
- the first dielectric layer comprises a spin-on dielectric, spin-on-glass, or flowable CVD oxide
- the second dielectric layer comprises a high density plasma (HDP) oxide and/or silicon nitride.
- HDP high density plasma
- FIG. 10 is a semiconductor structure in accordance with alternative embodiments of the present invention including a transistor.
- Semiconductor structure 400 includes a semiconductor substrate 402 and transistor 420 disposed on the semiconductor substrate 402 .
- the transistor 420 includes a gate stack 424 and source/drain region 422 a - b including stressor material 450 .
- the gate stack 424 includes a gate 430 over a gate dielectric 432 , such as silicon oxide, hafnium oxide, or zirconium oxide, and spacers 434 a and 434 b at each side of the gate 430 and gate dielectric 432 .
- the spacers can include a nitride or oxide such as silicon nitride or silicon oxide.
- a shallow trench isolation structure is disposed adjacent to the source/drain region 422 a .
- the shallow trench isolation structure includes a cavity 404 formed in the semiconductor substrate 402 , the STI cavity 404 comprising an upper region 411 and a lower region 413 .
- the upper region comprises a sigma cavity 408
- the lower region 413 comprises a substantially rectangular cavity 412 .
- a first dielectric layer 414 is disposed in the lower region 413
- a second dielectric layer 416 is disposed in the upper region 411 , and is planar with a top surface of the substrate 402 .
- the source/drain region 422 a - b further includes a compressive stress material and the second dielectric layer 416 includes a compressive stress material.
- the source/drain regions 422 a - b further include a tensile stress material and the second dielectric layer 416 includes a compressive stress material.
- the source/drain regions 422 a - b further comprise a tensile stress material and the second dielectric layer 416 includes a tensile stress material.
- the source/drain region 422 further includes a compressive stress material and the second dielectric layer 416 includes a tensile stress material.
- Embodiments of the present invention may be used with PFET (p-type field effect transistor) or NFET (n-type field effect transistor) devices.
- stressor material 450 may be comprised of silicon germanium for compressive stress.
- stressor material 450 may be comprised of silicon phosphorus, silicon carbon, or silicon carbon phosphorus for tensile stress.
- the upper fill material (second dielectric layer 416 ) and stressor material 450 may be of similar or opposite stress types (tensile or compressive). This allows tuning of the channel stress to accommodate design flexibility.
- FIG. 11 is a flowchart indicating process steps for embodiments of the present invention.
- a first etch in a semiconductor substrate is performed to form a cavity.
- the etch may be an anisotropic etch such as a reactive ion etch (RIE).
- RIE reactive ion etch
- a sigma etch is performed on the cavity to form an upper region of the cavity.
- the etch may be performed with a wet etch process utilizing, e.g., tetramethylammonium hydroxide (TMAH), ammoniumhydroxide, and/or potassium hydroxide (KOH).
- TMAH tetramethylammonium hydroxide
- KOH potassium hydroxide
- TMAH tetramethylammonium hydroxide
- KOH potassium hydroxide
- the etch may be an anisotropic etch such as a reactive ion etch.
- the lower region of the cavity is filled with a first dielectric material.
- the filling may be achieved by chemical vapor deposition.
- the first material may be spin-on-dielectric, spin-on glass, and/or flowable oxide.
- the first material is recessed.
- the recessing may be achieved by chemical mechanical planarizing (CMP) first and followed by reactive ion etching (RIE) or selective wet etch process.
- CMP chemical mechanical planarizing
- RIE reactive ion etching
- the upper region of the cavity is filled with a second material. This filling may be performed by various CVD methods.
- the second material may be HDP oxide or SiN for stronger residual stress.
- the second material may be planarized to a level flush with a top surface of the semiconductor substrate.
- the planarization may be achieved by chemical mechanical polish (CMP).
Abstract
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US9607847B1 (en) * | 2015-12-18 | 2017-03-28 | Texas Instruments Incorporated | Enhanced lateral cavity etch |
US10559490B1 (en) | 2018-08-21 | 2020-02-11 | Globalfoundries Inc. | Dual-depth STI cavity extension and method of production thereof |
CN110854060A (en) * | 2019-11-19 | 2020-02-28 | 上海华力集成电路制造有限公司 | STI structure and manufacturing method thereof |
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